My son and I built this kit as a minimum diameter rocket. And we never glassed the fins at all. I don’t remember who made the motor retainer (but it was like a snap ring retainer. But we have flown this rocket on H123’s and never had any problems. It was like about Mach speed by the time it left the rail. And then my son decided to fly it on a I211 and we know that it left the rail and we saw the tracking smoke. We know that it held together by the tracking smoke but after that quit smoking we lost sight of it and it really flew nice and we heard the ejection charge go off but it was so high up that we never found it at all. All I can say is this is a really nice kit for flying on small to I211 and like I was saying we never glassed the fins on and we never had a problem with it holding together. So we will be buying another kit soon because my son loves this kit.